Medical questions 4

Question 1

What is the difference between spasticity and rigidity?

Answer 1

Rigidity represents a constant increased tone throughout the range of movement and is independent of velocity. Spasticity represents increased tone that is velocity-dependent, being more marked at the onset of the movement and decreasing suddenly as passive movement is continued (clasp-knife phenomenon).

Question 2

What do you understand by the term transverse myelitis?

Answer 2

This is a broad term used to describe acute inflammation of the cord. Inflammation tends to involve the cord diffusely at one or more levels, affecting all spinal cord function, with resultant bilateral motor, sensory and sphincter deficit below the level of the lesion. Causes include:

• Bacterial infection e.g. Lyme disease, mycoplasma, TB, syphilis
• Viral infections
• Demyelination e.g. MS
• Radiation myelopathy
• Anterior spinal artery occlusion
• Vasculitis

Question 3

What is the pathophysiological basis of spasticity?

Answer 3

Spasticity results from enhanced stretch reflex activity, which may be manifest also by increased muscle tone and exaggerated reflexes. In upper motor neuron lesions, inhibitory inputs from the reticulospinal and other descending pathways to the motor and interneuronal circuits of the spinal cord are lost, resulting in alpha-motor neuron hyperexcitibility.

Question 4

What is a cerebellar nystagmus like?

Answer 4

A cerebellar nystagmus is a coarse horizontal nystagmus with the fast component towards the side of the lesion.

Question 5

What is pendular nystagmus a sign of?

Answer 5

Blindness

Question 6

What is gaze-evoked nystagmus?

Answer 6

This is a jerk nystagmus that occurs only when the eyes are moved into eccentric gaze. Common types are physiological nystagmus, cerebellar nystagmus and gaze-paretic nystagmus.

Question 7

What are the main structures in the cavernous sinus?

Answer 7

Cranial nerves III, IV, VI, Va and Vb
Sympathetic carotid plexus
Intracavernous carotid artery

Question 8

What is the ice pack test for myasthenia gravis?

Answer 8

An ice pack is applied to the ptotic eyelid for 2-5 minutes and improvement is noted in the ptosis. This test has a high sensitivity and specificity but may be difficult for the patient to tolerate.

Question 9

What is the pathophysiology of myasthenia gravis?

Answer 9

This is an autoimmune disorder characterised by antibodies directed against nAChR or the post-synaptic membranes of the NMJ.

Question 10

What treatment options are available for myasthenia gravis?

Answer 10

Acetylcholinesterase inhibitors
Immunosuppresive therapy
Plasma exchange
Intravenous immunoglobulin

Question 11

What is Foster-Kennedy syndrome?

Answer 11

This is ipsilateral optic atrophy, due to compression on the optic nerve, and contralateral papilloedema due to raised intracranial pressure. It is commonly caused by tumours on the inferior surface of the frontal lobe e.g. olfactory grove meningioma or medial third sphenoid wing meningioma.

Question 12

What is syringomyelia?

Answer 12

This is the development of a fluid-filled tubular cavity (syrinx) in the central area of the spinal cord and originates in the spinal cord tissue. The syrinx most often deveops in the cervical and thoracic segments of the spinal cord.

Question 13

What are the causes of syringomyelia?

Answer 13

CSF blockage: this is the commonest type. The most common cause is Arnold-Chiari malformation.

Spinal cord injury

Intramedullary spinal tumours

Idiopathic

Question 14

How do you explain the clinical signs seen in syringomyelia?

Answer 14

The syrinx extends through a segment of the spinal cord.

At the level of the syrinx - the anterior horns of the spinal cord are affected thus damaging the LMN at the corresponding levels. The decussating fibres of the spinothalamic tract are affected throughout the length of the syrinx whilst the posterior columns are relatively spared. This results in a dissociated sensory loss.

Below the syrinx - the corticospinal tracts are affected at the level of the syrinx. This results in UMN signs below the level of the syrinx.

Question 15

What treatments are available for syringomyelia?

Answer 15

Surgical treatments:
Cervical decompression
Dorsolateral myelotomy - the syrinx is drained into the subarachnoid space through a longitudinal incision.
Shunt formation

Question 16

Explain the swinging light test.

Answer 16

This is a reliable test for identifying a relative afferent pupillary defect. A light is shone into one eye and then quickly switched to the other and this is repeated back and forth. Under normal conditions, as light on one pupil will cause both pupils to constrict, both pupils should remain constricted throughout. In a RAPD, the optic nerve functions adequately to provide a direct reflex on the affected side and a consensual reflex on the opposite side. During the swinging torch test, when the light is switched back to the affected eye, the direct reflex is weaker than the consensual reflex. The consensual reflex from the opposite eye is eye dilatation, therefore the affected eye demonstrates abnormal pupillary dilatation when the light is shone onto the opposite side.

Question 17

Which nerve pathways are responsible for the light reflex?

Answer 17

Afferent: optic nerve -> lateral geniculate body –> midbrain

Efferent: Edinger-Westphal nucleus (midbrain) –> oculomotor nerve

Question 18

What are the causes of a RAPD?

Answer 18

Optic nerve disorders and retinal disorders?

Question 19

What is an Argyll Robertson pupil?

Answer 19

Both pupils are small and irregular, reacting to accommodation and not to light.

Question 20

What are the causes of Argyll Robertson pupils?

Answer 20

The most common cause is neurosyphilis. Other causes include diabetes, midbrain lesion, Lyme disease, Wernicke’s encephalopathy and brainstem encephalitis.

Question 21

What are the common causes of hemiplegia?

Answer 21

Cerebrovascular accident
Tumour
Demyelination
Abscess
Post-ictal (Todd's paresis)
Functional

Question 22

How do you differentiate between a cerebral and brainstem stroke?

Answer 22

Abnormalities of a higher function e.g. neglect, aphasia, apraxia, homonymous hemianopia and seizures all suggest a cerebral stroke.

Abnormalities of cerebellar function or eye movements or Horner’s syndrome, and the presence of crossed signs suggest a brainstem stroke.

Question 23

What is the significance of unilateral arm weakness being significantly greater than unilateral leg weakness or vice versa?

Answer 23

This functional distinction may indicate whether the middle or anterior cerebral artery is preferentially affected. MCA lesions predominantly affect the arm and face, and ACA lesions predominantly affect the leg. If both MCA and ACA territories are affect, this points to carotid artery stenosis that may warrant an endarterectomy.

Question 24

What are the features of Graves’ disease, independent of hyperthyroidism?

Answer 24

Goitre
Graves’ ophthalmopathy
Thyroid acropachy
Pretibial myxoedema

Question 25

What would you advise a patient who had recently received radioiodine?

Answer 25

Patient must avoid contact with children or pregnant women for 2 weeks.
Pregnancy must be delayed for four months following therapy.
The risk of developing hypothyroidism is 2-3% per year.

Question 26

What is the diagnostic test for adrenal insufficiency?

Answer 26

Serum cortisol - may be useful in excluding adrenal insufficiency but not as sensitive

9am cortisol greater than 500 nmol/l excludes adrenal insufficiency.

Dynamic testing is performed if 9am cortisol is equivocal. This involves the adminstration of 250mcg of synacthen and the measurement of ACTH and cortisol before, and at 30 and 60 minutes. Interpretation: impaired cortisol response and ACTH>200ng - primary adrenal failure. If ACTH<10ng/L, secondary pituitary adrenal failure.